In recent years, increasing endeavours have been made to automate and optimise processes for the manufacture of textile finishing and improving agents and their intermediates, e.g. dyes and fluorescent whitening agents, both as regards the manufacturing process itself as well as working up. To obtain satisfactory and reproducible results it is necessary to rely on analytical methods which are characterised by the following criteria: short duration of analysis, high frequency of analysis and greater information content per unit of time, as low costs as possible, simplicity, reliability, and minimum space requirements. Equipment that meets these requirements comprises in particular sensors for measuring physical parameters, e.g. temperature, pressure and consumption of starting materials.
These parameters, however, provide no information on the current state and condition of the process (yield of desired product, concentration of by-products, product quality) and the reaction course at any given time. Thus control and maintenance of constant product quality allied to optimum yield is not ensured. Further, it is not possible to make any prognoses from the physical parameters regarding the end point of a reaction, product quality, and yield. Up to now it has been customary to analyse the reaction mass at the end of a process step or at the end of the entire process, thereby ruling out in situ corrections during the reaction course.
Irrespective of the quality of the starting materials, uniform quality of the products of the process together with optimum yield is required at present time of continuous as well as discontinuous processes for the manufacture of textile finishing and improving agents as well as their intermediates.
Discontinuous (i.e. batch) processes in particular often result in products of variable quality induced by the varying quality of the starting materials, and the yield differs from batch to batch.
Accordingly, it is the objective of the present invention to provide an analytical method that meets the aforementioned requirements and to develop a method of controlling and optimising processes for the preparation of textile finishing and improving agents and their intermediates by means of said method, such that control and optimisation can also be carried out preferably on-line.
It has been found that the method of flow injection analysis is preeminently suitable for this purpose.
Flow injection analysis is an automated wet chemical technique based on continuous streams of reagents in capillary tubes, on the injection of reproducible samples into said streams, on the controlled dispersion of the sample zone on its path downstream to the detector, and on precise timing of a single analysis. A flow injection analyzer is characterized by a short start-up time, high injection frequency, and a precise knowledge of the state of the system before and immediately after the individual analysis (modulation).
Flow injection analysis is known per se and reference is made to the following literature: E. H. Hansen and J. Ruzicka "Flow Injection Analysis", John Wiley and Sons, New York, 1981; C. B. Ranger in "Automated Stream Analysis for Process Control", Vol. 1, page 39 et seq., D. P. Manka, Academic Press, 1982.
The primary field of use of flow injection analysis to date has been the automation of methods of wet chemical analysis in the laboratory. Flow injection analysis has also been used for monitoring a small number of continuous chemical processes.